An optical disc is a data storage medium in the form of a flat, circular structure, typically made out of a transparent plastic material, that incorporates a layer or layers that can be patterned with features that modulate the intensity of laser light reflected from the disc. The optical disc typically comprises a spiral pattern of such features that is addressed by light from a laser diode that is scanned along a radius of the disc as the disc is being rotated. Variations in the intensity of reflected light are detected and interpreted as individual bits. Since the features that can be written and detected may be extremely small, a great deal of data can be stored on an optical disc. Moreover, since optical discs may be cheaply manufactured, they may provide a very competitive cost per bit of data stored in relation to other storage media.
Several generations of optical disc technology have been developed. The compact disc (CD) is read with a near-infra-red-emitting laser and stores about 700 MB in a single layer. The DVD is read with a red-emitting laser and stores about 5 GB in a single layer, while a Blu-ray disc is read with a blue-emitting laser and stores about 25 GB in a single layer.
The standard optical disc is a polycarbonate disc of 120 mm diameter, but many other formats have been produced. Single-layer discs have one reading/recording face of high optical quality that is addressed by a laser, while the opposing face may be opaque and is available for labeling the disc.
Recordable and re-writable optical discs are widely available, but have the problem that it may be difficult for a user to label the disc with annotation of what has been recorded. A common practice has been to write onto the surface of the disc with a pen, but this may lead to a perception of a low quality. Several different approaches have been developed for high-quality labeling of a recordable optical disc with customized information, but all have some drawbacks. For example, it is possible to print a label (using, for example, an ink-jet printer) onto a substrate having a sticky back, and to append this label to the optical disc. There is a possibility, in this case, of applying the label eccentrically and unbalancing the disc, leading to problems in reading back the data. It is even possible that the label may be inadvertently applied to the wrong disc. Alternatively, as described in U.S. Pat. No. 7,036,131, an ink-jet printer may be built into the optical drive itself, and the disc may be pre-coated with an ink-receiving layer. In this case, however, the optical drive must be enlarged substantially so as to accommodate the ink-jet printer and ink supplies. An alternative approach is described in U.S. Pat. No. 6,864,907, in which there is described a method by which a thermally-sensitive layer is provided on the optical disc. After writing information to the optical recording surface, the disc is flipped over and re-inserted into the optical drive, whereupon the laser may be used to label the disc by activating the thermally-sensitive layer. This method has the disadvantage that the laser power in optical drives is quite low, and that therefore the time required to write the label may be on the order of several minutes. In addition, full-color printing may be difficult to achieve. U.S. Patent Application No. 2008-0111877 describes an optical disc bearing a full-color label intended for laser exposure. In this case a more powerful laser than is required for writing or reading information onto the data-storage layer or layers of this disc may be used, but such lasers may have prohibitive cost for use in consumer devices.
There therefore remains a need for a method of labeling an optical disc that does not require affixing a label to the disc, and that overcomes the above-mentioned disadvantages with existing integrated disc/label systems.